Archive for April, 2010

Went to roll the bike out of the garage and the rear tire was dead flat. You don’t even need to look at the tire, you just instantly know something’s wrong: the bike feels funny with a flat tire.

The picture shows the problem: a pinhole in the tube. Nothing penetrated the tire, nothing went wrong with the tire liner (you can see this was a few mm from the edge, so it’s not an abrasion flat), there are no problems anywhere. Just a tiny hole in the tube.

As nearly as I can tell, the tube simply failed at that point, without any external aggravation.

Popped in another tube and it’s all good, but … I guess it’s time to buy some new tubes: the new one came from a box dated May 90.

Finding a flat in the garage is much much better than finding a flat on the road.

The snows have retreated and it seems the mice have been busy tunneling in the back yard. If we cared more about the lawn, I’m sure I’d be outraged. As it is, the tunnels will be gone after a few mowings and life will move on.

I didn’t spot their grainery, but I’m sure the grass will be greener around the latrine…

Certainly these were different mice than the ones who made far more extensive living quarters out front, but they’re definitely relatives.

So Mary was going to apply the long-disused Sears Craftsman electric hedge trimmer to the decorative grasses she’d planted on either side of the (equally disused) front entry, but when I deployed the thing it didn’t run. A quick walk through the debugging tree: GFI green, extension cord OK, so it must be the trimmer.

Off to the Basement Laboratory Repair Wing…

Two tricks to getting it apart, after removing all the obvious screws:

The handle comes out of the sockets after great persuasion

Remove two of the three hex-head-with-lockwasher screws on the bottom and the case pops apart. The third screw holds the motor plate into that half of the case.

The switch is, of course, not intended to be repairable, but that’s something of a motivator around here. It uses those awful poke-and-pray spring clamps, which you could, in principle, release with a small screwdriver, but I cut the wires on the motor side of the switch, leaving plenty of room to graft connectors onto them.

Next time, I’ll be able to release the wires more easily.

Congealed grease on switch contacts

A rivet holds the switch together, but attacking it with a drill removed enough of the head that I could whack the rest of the body out with a drift punch. A 2-56 machine screw fits neatly into the hole and there’s enough clearance on both sides for the screw head and a nut; hack the screw to length with a Dremel abrasive cutoff wheel.

Notice that the switch trigger button visible from outside the case acts on a push rod that slides the movable contacts (in the top part in the picture) back-and-forth atop the copper contacts (with the wires). A pair of springs loads the movable contacts against the copper strips.

The problem turned out to be, as expected, congealed grease inside the switch. The black gunk on the right halves of the copper contacts was essentially solid; you can see that it formed a nice insulating layer. I cleaned that out, polished up the moving contacts, reassembled it, and … the switch still didn’t work.

At least I discovered that with an ohmmeter, before reassembling the entire trimmer!

Switch contact slider

The movable switch contacts have a small ramp, just about in the middle, that rides up on the black hump between the copper strips when the trigger button is released. That mechanically breaks the connection, but also allowed the grease to congeal in the air gap. The grease also formed a lump that prevented the movable contacts from pressing firmly against the copper strips, despite the springs.

I gnawed out that crud with a small screwdriver, dabbed on more contact oxidation prevention grease, buttoned it up again, and now the switch works perfectly again.

New switch wires

I spliced in somewhat longer lengths of hookup wire with butt-splice connectors I’ve had for years and it’s all good.

The post with the screw hole just below the wires matches another in the opposite half of the case; the post actually fits inside the ring you see here, so it doesn’t crunch the wire. However, the wire must be pushed in far enough to avoid interfering with the switch action rod.

I tote around an ancient Palm Zire 71, which suffices for my simple calendar & to-do lists. This is my second, as the first failed when the flexible cable connecting the guts to the charging / USB connector crapped out; turns out that the slide-to-open feature that reveals the crappy camera also stresses the flexy cable to the breaking point. Now I don’t do that any more.

The battery (well, it’s actually a single Li-Ion cell, but let’s not be pedantic) finally stopped taking a charge, so I did a full backup, tore the thing apart, and popped in a new battery. This being my second Zire 71, things went smoothly…

I got a stack of surplus Palm batteries some years ago, but they’re readily available from the usual suspects for prices ranging from $5 to $50. We’ll see how well mine survived their time in isolation.

The connectors don’t match, which means you just chop off them in mid-wire, then solder the old connector onto the new battery. A few dabs of Liquid Electrical Tape and it’s all good.

I used a pair of blue LEDs for the colon in the Totally Featureless Clock. Each one has a brass tube to define the dot and a white plastic diffuser to eliminate hotspots.

Some rummaging in the brass cutoff assortment produced a pair of tubes with a 0.300 inch ID that closely matched the width of the LED segment bars. The catch is that I don’t have a core drill that spits out 0.300 inch slugs…

Milling the dots

So I taped a chunk of translucent acrylic to some plywood scrap and milled the dots. Helix milling on the lesser of a 4% slope or 1/5 of the cutter diameter, 15 inches/min, no cooling, maybe 1500 rpm.

The resulting disks were snug slip fits into the tubes, although I added a dot of cyanoacrylate to ensure they didn’t get any ideas about perpetrating an escape.

It took two disks to remove all the hotspots, which reduced the light intensity to the point where I had to increase the LED current, which really heated up the linear regulator driving the dots. Fooey! In retrospect, I think frosting the LED lens would eliminate the need for a second diffuser without decreasing the intensity much at all.

The latch closing my tea ball consists of a nice stainless steel dingus held on by a grotty rivet of unknown provenance that I’ve repeatedly staked over the years. It finally came undone this morning, so I had a few minutes of Quality Shop Time right after breakfast.

My tiny-screw box (left over from the long-gone Leichtung Workshops) has some stainless 0-80 screws that I found somewhere, but only brass nuts. Ah, well, we used to use brass water fixtures and lead pipe, so an 0-80 nut in hot water isn’t going to kill me.

The ball rim has a recess for the rivet head, but the screw head was slightly larger. I braced the rim of the ball across the vise jaws and give the recess a few shots with a fat punch to enlarge it.

Stainless screw and brass nut

Then…

A dot of Loctite on the threads

Assemble everything

Take it apart to put the latch on the correct side of the rim

Reassemble

Attempt to close

Gently bend the rim to flatten it out

Close

Attempt to latch

Brace closed rim on vise opening with screw head up

A few shots with a drift punch to settle recess around screw head

Success!

It seems I ain’t worth a damn in the morning without a hot cuppa. The rituals must be preserved.

One a day, every day…

Redshifting

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